Traditional film-screen radiography has been used as a medical imaging diagnostic system for many years. X-rays are projected through a patient's body part to form a latent radiographic image on film contained in a cassette. The film is then be chemically or thermally processed to produce a visual radiographic image which can be used by a health care professional for diagnostic purposes. The delay in obtaining a diagnostic image, the use of a chemical or thermal processor, and the difficulty in providing the radiographic film outside of the immediate medical facility, has resulted in the development of digital radiographic imaging systems. Computed radiography (CR) digital systems have been developed in recent years that provide reusable CR plates which are scanned to produce a digital radiographic image. The CR systems still result in a delay in obtaining a diagnostic image due to the necessity of scanning an exposed CR plate.
Digital radiography is achieving a growing acceptance as an alternative to film-screen and CR radiography systems. With digital radiography (DR), the radiation image exposures captured on radiation sensitive layers are converted, pixel by pixel, to digital image data which is stored and subsequently displayed on electronic display devices. One of the driving forces in the success of digital radiography is the ability to rapidly visualize and communicate a radiographic image via networks to a remote location for analysis and diagnosis by radiologists without the delay in sending chemically or thermally processed radiographic films by courier or through the mail. The use of chemical or thermal processors is also eliminated by digital radiography systems.
The solid-state, ionizing radiation based image detectors used in projection digital radiography today are relatively large, heavy, and expensive. Additionally, a complete DR systems using this type of detector (hereafter DR detector) requires substantial capital investment to retrofit with existing X-ray equipment. For projection radiography, the detector array in these systems is typically a large-area pixilated device, fabricated on a glass substrate. The large-area detector array is expensive to fabricate, and it is also fragile to handle since the substrate is glass. As a result, DR detectors and systems are very expensive and the current market is small given the high cost of investment.
DR detectors can either be direct or indirect conversion devices. Direct detectors use a material such as selenium in contact with a TFT array for conversion of X-ray photons. Indirect detectors use a scintillator screen for conversion of X-rays to visible light, through contact with a silicon photodiode and TFT array.
The dimensions of medical radiographic cassettes/screens/films are specified under ISO 4090:2001(E) standard. This includes both conventional film and CR phosphor screens, with nominal imaging areas up to 35 cm×43 cm and 40 cm×40 cm (metric origin). Standard cassette dimensions are also specified as part of the ISO standard, including the maximum cassette thickness of 16.0 mm.
U.S. Pat. No. 5,844,961, issued Dec. 1, 1998, inventors McEvoy et al., discloses a filmless digital x-ray system that uses a standard x-ray cassette housing. An external power source provides the power for the detector and associated electronic system.
U.S. Patent Application Publication No. 2004/0227096, published Nov. 18, 2004, inventor Yagi, discloses a metal spring assembly for providing shock isolation to a radiation detector that provides limited shock isolation due to the stiffness of the metal type spring.
U.S. Patent Application Publication No. 2005/0017188, published Jan. 27, 2005, inventor Yagi, discloses means to provide shock isolation to a radiation detector, in which shock absorption material is provided between inner and outer frames. This structure increases the size of the cassette.
U.S. Pat. No. 6,296,386, issued Oct. 2, 2001, inventors Heidsieck et al., discloses a cassette for producing images for a radiography apparatus intended for mobile type cassettes. A handle and locking means are disclosed for locating the cassette within a reception housing. It is intended for use with mammography exposure devices, where locking features are advantaged since the reception housing can be in multiple orientations, where the cassette would be susceptible to dropping. The features disclosed are larger than the standard cassette and extend to contact the reception housing. This can limit its usage to specific types of x-ray equipment.
U.S. Pat. No. 6,855,936, issued Feb. 15, 2005, inventor Yamamoto, discloses a cassette for use in a portable imaging environment. The cassette has a plurality of electrical connecting ports and a plurality of fixed handles. These allow for multiple detector orientation for specific radiographic exposures.
U.S. Pat. No. 6,805,484, issued Oct. 19, 2004, inventors Kuramoto et al., discloses a portable device with at least one handle secured to the device housing. This handle is movably connected or pivoted, for the purpose of facilitating patient positioning only.
U.S. Pat. No. 6,700,126, issued Mar. 2, 2004, inventor Watanabe, discloses a radiation detector which includes a shock absorber placed on any one of the side walls of the cassette. While this provides some lateral protection to the detector, it does not provide protection in the direction orthogonal to the detector plane.
Accordingly, there is a need for a DR detector system that provides a compact encasement for housing the glass detector and supporting electronics so that it fits within the volume of existing standard film cassettes and meets the requirements of the ISO standard. There is also a need for a durable structure that protects the fragile detector from damage, due to physical shock or loads applied externally to the encasement. It is also desirable that the DR detector be usable for both typical x-ray exam room procedures as well as with portable imaging equipment. There is also a need that the detector be wireless, especially for portable imaging equipment where any electrical cables can interfere with user operation and handling of the portable detector.